From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: Scott Carey <scott@richrelevance.com>
Cc: jd@commandprompt.com
Cc: pgsql-performance@postgresql.org
Subject: Re: Create and drop temp table in 8.3.4
Date: Thu, 06 Nov 2008 15:49:59 -0600
Message-ID: <49131226.EE98.0025.0@wicourts.gov> (raw)
In-Reply-To: <a1ec7d000811061305n7b28800od469c1411e1a9928@mail.gmail.com>
References: <4911957A.EE98.0025.0@wicourts.gov>
<4911D4DB.EE98.0025.0@wicourts.gov>
<4912EAFF.EE98.0025.0@wicourts.gov>
<1225999071.1204.14.camel@jd-laptop.pragmaticzealot.org>
<4912F29E.EE98.0025.0@wicourts.gov>
<a1ec7d000811061305n7b28800od469c1411e1a9928@mail.gmail.com>
>>> "Scott Carey" <scott@richrelevance.com> wrote:
> Note that Write Barriers can be very important for data integrity
when power
> loss or hardware failure are a concern. Only disable them if you
know the
> consequences are mitigated by other factors (such as a BBU + db using
the
> WAL log with sync writes), or if you accept the additional risk to
data
> loss.
For those using xfs, this link may be useful:
http://oss.sgi.com/projects/xfs/faq.html#wcache> On Temp Tables:
> I am a bit ignorant on the temp table relationship to file creation
-- it
> makes no sense to me at all that a file would even be created for a
temp
> table unless it spills out of RAM or is committed. Inside of a
transaction,
> shouldn't they be purely in-memory if there is space? Is there any
way to
> prevent the file creation? This seems like a total waste of time for
many
> temp table use cases, and explains why they were so slow in some
exploratory
> testing we did a few months ago.
As I learned today, creating a temporary table in PostgreSQL can
easily create four files and do dozens of updates to system tables;
that's all before you start actually inserting any data into the
temporary table.
-Kevin
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To: pgsql-performance@postgresql.org
Cc: Kevin.Grittner@wicourts.gov, scott@richrelevance.com, jd@commandprompt.com
Subject: Re: Create and drop temp table in 8.3.4
In-Reply-To: <49131226.EE98.0025.0@wicourts.gov>
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